Java 'Error: Could Not Find or Load Main Class': How to Fix Classpath Issues?

Java Class Not Found: Resolving "Error: Could Not Find or Load Main Class"

When attempting to run a Java program, you may encounter the error "Error: Could not find or load main class." This issue typically indicates that the Java Virtual Machine (JVM) cannot locate the specified class file containing the main() method.

To resolve this problem, ensure that the classpath is correctly configured to include the directory containing the .class file. In the given scenario, you are compiling multiple Java files (e.g., SpatialModel.java, VensimHelper.java) into .class files.

Verifying Classpath

The classpath specifies the directories from which the JVM can load classes. To verify the classpath, execute the following command in your terminal:

echo $CLASSPATH

This command will display the current classpath settings. If the directory containing your .class files is not included, you need to add it.

Correcting Classpath

Add the current directory, where the .class files reside, to the classpath using a period (.) as a separator. For example, if your .class files are in the current directory, execute the following command (replace username with your actual username):

CLASSPATH=.:/home/username/project/vensim.jar:/home/username/project/apache-log4j-1.2.16.jar
export CLASSPATH

Running the Program

After updating the classpath, you should be able to run your program. For the provided code, execute the following command:

java -cp .:vensim.jar:apache-log4j-1.2.16.jar SpatialModel vars

Windows Users

Note that in Windows, the classpath separator is a semicolon (;) instead of a period (.). For Windows users, the classpath setting would look like the following:

CLASSPATH=.;C:\Users\username\project\vensim.jar;C:\Users\username\project\apache-log4j-1.2.16.jar

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